"Our goal is, very simply, to breach the legal wall that separates all humans from all nonhuman animals," the charity said.

"Once this wall is breached, the first nonhuman animals on earth will gain legal "personhood" and finally get their day in court -- a day they so clearly deserve."

The group is seeking an order, on behalf of four chimps, for their release to a sanctuary to live out their lives with other primates in a natural outdoor setting.

The first of the suits have been filed in a New York court on Wednesday on behalf of Tommy, a 26-year-old chimp who is being held in the state

The lawsuit seeks a declaration that the "detention" of Tommy in a "small, dank, cement cage in a cavernous dark shed" is unlawful as the animal is a "legal person" with the "fundamental right to bodily liberty".

It demands his immediate release to a primate sanctuary.

The lawsuits include affidavits from scientists who say chimpanzees have complex cognitive abilities, such as awareness of the past and the ability to make choices, and display complex emotions such as empathy.

"Once we prove that chimpanzees are autonomous, that should be sufficient for them to gain legal personhood and at least have their fundamental interests protected by human rights," Mr Wise said.

If the lawsuits succeed, similar ones could eventually be filed on behalf of other species considered autonomous, such as gorillas, orang-utans, whales, dolphins and elephants, he said.